In recent years, there have been cases such that electronic devices such as servers are managed collectively in a data center or the like. With reference to FIG. 9, an exemplary configuration of a data center will be described. FIG. 9 is a diagram illustrating an exemplary configuration of a data center. As illustrated in FIG. 9, in a data center 901, a plurality of racks 902a to 902f are installed in columns with front surfaces and rear surfaces thereof facing the same directions, respectively. Then, a plurality of electronic devices such as servers are installed in each of the racks 902a to 902f. 
Moreover, in an electronic device such as a server, an amount of heat generation in an electronic component such as a CPU (central processing unit) has been continuously increasing. If a temperature of an electronic component as represented by a CPU becomes high, the electronic device may be operationally unstable. Therefore, in the data center, the electronic components are appropriately cooled so that the electronic devices can operate stably.
In the example illustrated in FIG. 9, cooling air of 20 to 25° C., for example, is blown out from an under floor 903 by an air-conditioning equipment 904, and is supplied to the racks 902a to 902f via floor surface apertured panels 905. The electronic devices mounted in the racks 902a to 902f rotate fans included therein to take in the cooling air from outside of housings of the electronic devices, thereby cooling the electronic components within the housings.
An amount of heat generation in a CPU changes in accordance with an amount of processing load. Therefore, in the data center, the electronic device changes the number of revolutions of the fan in accordance with the amount of heat generation in the CPU so as to change an amount of cooling air to be taken in from outside of the electronic device. For example, the number of revolutions of the fan is set in accordance with an intake air temperature of the electronic device or a CPU temperature.
Patent Literature 1: Japanese Laid-open Patent Publication No. 11-264599
Patent Literature 2: Japanese Laid-open Patent Publication No. 02-123413
However, the above-described conventional technique has a problem that there is a case where it is not possible to prevent an increase in electronic component temperature.
Specifically, in the conventional data center, a sufficient amount of cooling air has been supplied to racks via floor surface apertured panels with respect to an amount of cooling air taken in inside the housings of the electronic devices by the electronic devices. Thus, the electronic devices take in inside the housings thereof the cooling air supplied to the racks via the floor surface apertured panels, thereby appropriately cooling the electronic components of the electronic devices.
In recent years, however, a rack in a data center mounts a blade server having an improved processing capability and a larger amount of heat generation as compared to a conventional server. In such a data center, there is a case where an amount of air taken in by electronic devices becomes greater than cooling air supplied to the racks via the floor surface apertured panels. In such a case, there occurs a hot spot phenomenon such that warm exhaust air exhausted by the electronic devices is taken in again by the electronic devices together with the cooling air supplied to the racks. Such a situation that discharge from an electronic device is taken in again by the electronic device is called “exhaust air recirculation.”
Since the conventional data center does not deal with the possibility of an environment in which exhaust air recirculation occurs, exhaust air recirculation cannot be eliminated. Therefore, if a hot spot phenomenon is generated, even when the number of revolutions of the fan is increased so as to increase an amount of cooling air to be taken in by the electronic device, the electronic device takes in exhaust air therefrom together with the cooling air. Thus, due to the exhaust air from the electronic device, a temperature of the cooling air taken in by the electronic device increases. As a result, it fails to appropriately cool the electronic component and the temperature thereof thus increases.
With reference to FIG. 10, there is illustrated an example. FIG. 10 is a diagram illustrating changes in an electronic component temperature when the number of fan revolutions is varied in a data center where racks having blade servers mounted therein are arranged. In cases of the number of revolutions R1 to R3 illustrated in FIG. 10, an amount of cooling air supplied to the racks via the floor surface apertured panels is sufficient for an amount of cooling air taken in by the electronic devices. In such a case, by increasing the number of revolutions from R1 to R2, and then to R3, an air volume of the electronic device increases, and the electronic component temperature is therefore decreased from 98° C. to 71° C.
On the other hand, in cases of the number of revolutions R4 to R7 illustrated in FIG. 10, an amount of air taken in by the electronic devices becomes greater than the cooling air supplied to the racks via the floor surface apertured panels. In such a case, exhaust air recirculation occurs, and the electronic component temperature is increased from 86° C. to 90° C. Thus, in the conventional data center, it is not possible to prevent an increase in electronic component temperature when there is exhaust air recirculation.